1. Field of the Invention
The present invention relates to a method of detecting specific target DNA sequences, and in particular to the products of amplification reactions, as well as to reagents and apparatus used in that method.
2. Description of the Related Art
Many methods are known in order to detect the presence of particular target DNA sequences in a sample. A substantial proportion of these methods require that the DNA is denatured to single stranded form and then this sequence is hybridised or otherwise allowed to bind to a labelled sequence specific probe.
The target sequences are frequently subjected to amplification reactions, for example the polymerase chain reaction or the ligase chain reaction, in order to increase the amount of the target sequence to detectable levels.
Other methods of detecting sequences include the use of intercalating dyes which are incorporated into the sequences during the amplification reaction. However such methods are relatively non specific as the dyes will intercalate with any amplification product, even if they are the result of non-specific amplification products.
Other assays such as the TAQMAN™ assay utilise complex probes which include reporter and quencher moieties during the course of the amplification process. These probes hybridise to single stranded target sequences during the amplification reaction and are then digested by the enzymes carrying out the reaction. The relationship between quencher and reporter molecule of the probe produces a signal which can be monitored. The probes used in this case however, are complex and expensive.
It is known that peptide nucleic acids will strand invade DNA at purine rich sites to form triplex structures (P. E. Nielson et al., Science, 1991, 254, p 1497-1506, Turney D. Y. et al., Proc. Natl. Acad. Sci. USA, 1993, 90, 1667-1670). The mechanism by which this is effected is illustrated diagrammatically hereinafter in FIG. 1.
The applicants have found that this phenomenon can be used in detection of target DNA sequences.